Flexible bazooka balun



Dec. 27, 1960 P. F. EILAND, JR 2,966,640

FLEXIBLE BAzooKA BALUN Filed May 29, 1958 4 2 B Il Z5 4 MMM# ATTORNEYSpar.

United States Patent O FLEXIBLE BAZOOKA BALUN Phillip F. Eiland, Jr.,State College, Pa., assignor, by mesne assignments, to HRB-Singer',Inc., State College, Pa., a corporation of Delaware Filed May 29, 1958,Ser. No. 738,771

'1 Claim. (Cl. S33-26) This invention relates to line balance convertersand more particularly to baluns or bazooka type of line balanceconverters.

It is well known that standing waves are detrimental to the satisfactoryoperation of a radiation system. Balance converters have been developedwhich permit the connection of an unbalanced circuit such as a groundedtransmission line to a balanced circuit such as an antenna. One of themost commonly employed line balance converters for use with a coaxialtransmission line is a bazooka type line balance converter or balun.Conventional baluns are basically sections of rigid hollow cylindershaving a length of approximately one quarter of the operatingwavelength. The hollow cylinder or pipe is concentrically disposed aboutthe coaxial transmission line. One end of the pipe is in line with thetermination of the transmission line and the other end of the pipe isconductively connected to the outer conductor of the transmission line.Such baluns are both bulky and heavy and do not lend themselves topositioning on a curved transmission line.

It is accordingly an object of the invention to provide a line balanceconverter which is very compact and light in weight.

It is another object of the invention Ito provide a flexible balun whichcan follow a curved section of tiexible coaxial transmission.

It is another object of the invention to provide a balun having a Qlower than the Q of conventional baluns to permit the transmission of awider bandwidth of signal frequencies.

It is a general object of the invention to satisfy the other objects ofthe invention with a balun which is tlexible, inexpensive, light inweight, and easily maneuverable on a transmission line of curvedconfiguration.

Other objects and various further features of novelty land inventionwill be pointed out or will occur to those skilled in the art from areading of the following speciiication in conjunction with theaccompanying drawings which show, for illustrative purposes only, apreferred form of a line balance converter in accordance with theinvention. In said drawings:

Figure 1 is a longitudinal section of a coaxial transmission line andthe inventive balance converter;

Figure 2 is a perspective view of the line balance converter of Fig. 1operatively positioned on a section of coaxial transmission line;

Figure 3 is a schematic diagram of the line balance converter and itsassociated section of coaxial transmission line;

Figure 4 is the equivalent circuit diagram of the line balance converterof Fig. 1.

Briey, the invention contemplates a coaxial transmission line having aninner conductor and an outer conductor. Associated with the transmissionline are a transmission end for transmitting signals along the line anda termination end for receiving signals transmitted along the line. Aexible sheath of conductive material is concentrically disposed about alength of the transmiss iQn line. One end of the exible sheath issecured to the insulation surrounding the outer conductor of thetransmission line adjacent to the termination end. The other end of theflexible sheath is conductively coupled to the outer conductor of thetransmission line at a pointy spaced from the termination end.

More particularly, referring to Figures 1 and 2, a line balanceconverter 10 is shown operatively disposed with respect to a coaxialtransmission line 12 for coupling an unbalanced circuit to a balancecircuit. The coaxial transmission line 12 comprises an inner conductor14 concentrically encased by a tube 16 of an insulation material such aspolyethylene. `The outer conductor 18, concentrically disposed about thetube 16, is, in general, a very dense braid of thin wires. insulatingmaterial concentrically envelops the outer conductor 18. Terminals 22and 24 associated with a con-.

ventional R-F connector 26 (Fig. 2) respectively couple the innerconductor 14 and the outer conductor 18 to an' unbalanced load.Similarly, the terminals 28 and 30 (Fig. 1) associated with aconventional R-F connector 32 (Fig. 2) respectively couple the innerconductor 14 and the outer conductor 18 to a balanced load circuit.

The balanced line converter 10 is characterized by a liexible braidsleeving 34 woven of tine wire conductors. A collar 36 attached to oneend of the braid sleeving 34 is slidably, but tightly, secured to thecasing 20 at the termination end 38 of the coaxial transmission line 12.The braid sleeving 34 is stretched to hug the casing 20. Acircumferential gap 40 in the casing 20, exposing the outer conductor18, accommodates a section of the braid sleeving 34 to provide anelectrically conductive connection therebetween; metal collar 42maintains the connection.

As shown in Fig. 2, a plurality of gaps may be provided selectively tolocate the sleeve 34 along given different lengths of the line. Further,an elongated gap may be utilized to provide a slidable adjustment alongthe line.

When the impedances of the balanced and unbalanced circuits are alreadymatched, no impedance transformation is required and the balanced lineconverter 10 acts as a 1:1 transformer as shown in the equivalentcircuit diagram of Figure 4.

Basically, the line balance converter 10 (Fig. 3) is a quarter-waveshield which is placed around the termination end 38 of the coaxialtransmission line 12. A new section of coaxial transmission line isformed. This new section is a closed-end quarter-wave section 44 ofcoaxial transmission line Whose inner conductor is the outer conductor18 and whose outer conductor is the braid sleeving 34. In general, theouter conductor 18 is grounded. Therefore, since a high impedance existsbetween the braid sleeving 34 and the outer conductor 18, the section ofthe outer conductor 18 in the region of the termination end 38 is at ahigh impedance with respect to ground. Since the inner conductor 14 isalready at a high impedance with respect to ground, the terminals 28 and30 are at high impedance with respect to ground. If the terminals 28 and30 are connected to a balance circuit, the inner conductor 14 and theouter conductor 18 will assume equal impedances with respect to groundand the braid sleeving 34 will be at ground potential.

It should be noted that the length of the sleeving is given as a quarterof an operating wavelength (A). An effective quarter wavelength is theproduct of a quarter wavelength in free space and the propagation factorof the intervening medium. For common plastic insulations, such aspolyethylene, the propagation factor is 0.52. Thus theraxial length ofthe braid sleeving 34 is approximately an eighth of an operatingwavelength.

Further, since the braid sleeving is not a continuous conductor. it hashigher resistive losses than a conventional pipe type bazooka. In otherwords, it has a lower A casing 20 of au Q than the conventional linebalance converter. It should be noted that a lower Q permits thetransmission of a wider band of signal frequencies; in manyapplications, therefore, where the added band widthis required the lowerQ is an advantage.

There has thus been shown a line balance converter which is on the onehand light and compact and on the other hand llexible enough to follow acurved section of flexible transmission line. Furthermore, the disclosedbalanced line converter is inexpensive, extremely easy to construct andeasily maneuverable on the transmission line.

While the invention has been described in detail in connection with thepreferred form illustrated and disclosed, it will be understood thatmodications may be made within the scope of the invention as defined inthe claim which follows.

I claim:

A coaxial transmission line balance converter to provide a ilexibleconnection between a balance circuit and an unbalanced circuitcomprising a central conductor of flexible electrically conductivematerial having a predetermined length, a first sleeve of exibleelectrically insulating material disposed about said central conductorand extending continuously throughout its length, a second sleeve ofexible electrically conductive material disposed about said lrst sleeveand extending continuously throughout its length, a third sleeve ofexible electrically insulating material disposed about said secondsleeve and having a plurality of gaps spaced apart and extending apredetermined distance along said length, a fourth sleeve of exibleelectrically conductive material disposed about said third sleeve andextending continuously along said predetermined distance, and removableclip means to connect said fourth and said second sleeves electricallyat a selected one of said gaps.

References Cited in the file of this patent UNITED STATES PATENTSPeterson Aug. 9, 1949 Brown Aug. 8, 1950 Cox Aug` 12, 1958

